A carbon nanotube composed of only carbon atoms is a material having excellent electrical properties, thermal conductivity and mechanical properties. Carbon nanotubes are extremely lightweight, very tough and have excellent elasticity and restoration properties. Carbon nanotubes having excellent properties as described above are an attractive substance and very important as an industrial material.
A carbon nanotube composite material and conductive material obtained by blending a conductive filler in a polymer foam and elastomer are widely used in a variety of applications, for example, as a gasket and seal for providing electromagnetic shielding and/or electrostatic dissipation in electronic products, computers, and medical devices. In the past, electrical conductivity was usually provided by using fine particles such as metal or carbon black. As the increase in the miniaturization of electronic components and use of plastic parts, a carbon nanotube composite material and conductive material having a higher conductivity have been required in consumer electronics in particular. Therefore, carbon nanotubes having excellent conductivity are attracting attention as a conductive filler.
For example, when carbon nanotubes having carbon fibers extending three-dimensionally (radially) from a center portion are incorporated into an elastomer, the specific carbon nanotubes described above derive from this three-dimensional shape and as a result of being uniformly dispersed in the elastomer, a continuous conductive path is formed in the entire elastomer and flexible electrodes having excellent electrical conductivity are realized (Japanese Laid Open Patent No. 2008-198425).
In addition, a carbon nanotube composite material and conductive material including a carbon nanotube rubber composition comprised from a carbon nanotubes, an ionic liquid and rubber having miscibiloity with the ionic liquid has a sufficient conductivity of 1 S/cm or more and elongation of 10% or more for use as a material in electronic circuits and was used as wiring in stretchable electronic devices which can be used as flexible electronics (International Publication WO2009/102077).
However, because a conductive filler of the carbon nanotube composite material and conductive material according to these prior art can not completely follow the deformation of a matrix when stress such as strain is applied repeatedly, there is a problem whereby the structure of the conductive path of the conductive filler in the matrix gradually and irreversibly changes which deteriorates conductivity. For example, in the case of a carbon nanotube composite material and conductive material using the ionic liquid, carbon nanotubes and rubber described above, the ionic liquid is adsorbed around the carbon nanotubes, and carbon nanotubes are well dispersed in the matrix. However, when ionic liquid is present in a liquid state at the interface of the carbon nanotubes and the rubber, good stress transfer of the carbon nanotubes and rubber is prevented. As a result, in the case where repeated stress is applied, the ionic liquid begins to seep and the interface between the carbon nanotube and rubber structurally changes and conductivity deteriorates. Therefore, in Tsuyoshi Sekitani et al, A Rubberlike Stretchable Active Matrix Using Elastic Conductors, SCIENCE, 2008.9.12, vol. 321, p. 1468-1472, by opening a plurality of holes by punching the carbon nanotube composite material and conductive material and covering the carbon nanotube composite material and conductive material with a PDMS rubber, mechanical durability is improved.
In this way, a carbon nanotube composite material and conductive material having a high conductivity and excellent mechanical durability without any special treatment does not exist in practice and thus the appearance of this type of carbon nanotube composite material and conductive material is desired.